OK - I can tell you where you can get some information, but it does take a bit of work on your part. Since W&A Gilbey is a Diageo company, you'll need to contact Christine - their Archive Manager.
Send pictures of your bottle - clearly
showing all labels and the closure being used, and she will see what information she can find for you. I have already contacted her and she's expecting to hear from you.
We'd love for you to post her findings on our Whisky.com Forum so that all others seeking the same information can find it here!
Best of luck to you!